oestrus /(?)/

oes·trus

oestrus

n.
  1. A genus of gadflies. The species which deposits its larvae in the nasal cavities of sheep is oestrus ovis. (Zool.)
  2. A vehement desire.
  3. The periodical sexual impulse of animals; the period during which female animals are most receptive to males; heat; rut. (Physiol.)